(1) Field of the Invention
The present invention relates to line switching equipment and, particularly, to line switching equipment to be used in a data communication system including a personal line and a backup ISDN line, for switching the personal line to the backup ISDN line when a failure of the personal line occurs.
(2) Description of the Prior Art
Conventionally, line switching equipment for backup purpose of a personal line selectively connects data terminal equipment to data circuit terminating equipment (DCE) of a personal line or an ISDN terminal adapter of an ISDN line. The line switching equipment comprises a DTE interface portion coupled to the DTE, a DCE interface portion connected to the DCE, a terminal adapter interface portion connected to the ISDN terminal adapter, a switching portion for switching the DTE interface portion for switching the DTE interface portion to either the DCE interface portion or the terminal adapter interface portion and a control portion controlling the switching portion manually.
In a data communication system having such line switching equipment as mentioned above, when an operator on the local side detects failure of the personal line, he operates a switch of the ISDN terminal adapter on the local side to send a call therethrough to connect it to an ISDN terminal adapter connected to the line switching equipment on the remote side. When the operators on the both sides recognize that the line switching equipment on both sides have been connected to each other through the ISDN, they manually operate the control portions of the respective line switching equipment to signal a switching request to the respective switching portions. Upon this signal, the line switching equipment on the both sides switches the connections of the respective data terminal equipment from the personal line side to the ISDN line side to establish a backup network using the ISDN.
The conventional line switching equipment mentioned above, however, requires a human operator on each side for the manual switching operation, and the procedure necessary to establish the backup system is complicated and time-consuming. Further, ISDN terminal adapters are necessary to use the ISDN. In addition, it is impossible to send control information and/or alarm information during data communication through the ISDN circuit.